Sony vegas sound problem.

Hey guys, first thread here.

I recorded a a .avi file with Fraps from a game (Flight Simulator x) and wanted to put it in Sony Vegas to edit it, how ever there was no sound, quick visit to google told me that .avi files had problems in Vegas and you should convert the video, so I "tried" to convert the video into a HD mp4,wmv, mpg, mpg2, h.264 and whatever HD extension there is. problem here was that the converter keeps failing to covert my files.
So i got the perfect solution, or at least I thought: convert the video file to a .ac3 dolby digital file! how ever... sony vegas won't accept .ac3 files. Tried to convert it to a .AAC file, wont accept it either.
So I'm kinda outa good thoughts here and would like to hear you're opinion on it.